Open cast mining operations are well known and are conducted in a number of countries around the world. Typically they comprise progressively mining domains of an ore body in a staged batch-like process. Each so called batch comprises selectively placing explosives in the rock of the batch. Thereafter the rock is blasted to break and loosen the rock and form a muck pile. Typically the deposits in these mines are heterogeneous in the sense that the ore is disseminated in complex shaped volumes of varying grade within a host rock which is waste. The shape of each ore zone on a horizontal plane is represented by a polygon when viewed in plan.
The rock body for example might comprise one or more ore polygons that are economic to recover and waste rock that is to be discarded. The ore is selectively removed from the muck pile and sent to a concentrator where the valuable mineral is extracted by an appropriate technique. Similarly the waste rock is removed and sent to a discard rock dump. Clearly an important part of this process is the accurate delineation of and identification of the boundaries between high grade ore and low grade ore and between ore and waste. A mixture of scientific know how, geology, computer modelling, and experience is used to determine the boundaries in the body of rock prior to blasting being conducted. This art has developed to the point where mining engineers and geologists have a good three dimensional picture of the boundaries between the different ores in the virgin rock prior to blasting.
However it is quite clear that the rock moves when it is subjected to blasting. The blasting causes some expansion of the rock and in addition there may be some differences in the amount of movement of the different parts of the rock. This is illustrated schematically in FIG. 1. Currently there are no satisfactory techniques for measuring or modelling this movement in the rock and thereby also the ore boundaries as a result of the blasting operations. Mining engineers and geologists sometimes work on the assumption that the ore boundaries of the blasted rock are the same as that for the unblasted rock and direct the broken rock to respectively the concentrator and the dump on this basis.
The problem is that it is clear that the rock and therefore also the ore boundaries do move. Accordingly if this movement is not accounted for by the mining engineers in the mining operation some of the ore is directed to the dump. This leads to a loss of product which is intended to be recovered. Similarly some of the waste is recovered in the ore stream and is sent to the concentrator. This can lead to a significant loss of efficiency in the concentrators as it processes more waste and less product. This can lead to a drop off in the volume of concentrate produced per unit time.
It is universally recognised that this approach is unsatisfactory. It would therefore be highly desirable if a way could be devised of measuring the movement of the rock and thereby the ore boundaries. It would enable a three dimensional picture of the ore boundaries in the pre-blast rock body to be adjusted to account for the measured rock movement. This in turn would improve the correct reporting of the ore to the concentrator and the waste to the dump.